The metabolic and behavioral characteristics of early onset hypercellular obesity will be studied in the genetically obese Zucker (fa/fa) rat. The relationship between metabolic alterations accompanying hypercellular obesity in the Zucker "fatty" rat and the feeding behavior of the fatty during growth and in adulthood will be examined. Specifically, changes of food intake and food motivated behavior observed during growth will be correlated with changes of body composition, adipose tissue cellularity, plasma hormone profiles, and fat synthesizing and storing enzymes. We will attempt to alter the body composition and degree of hyperphagia of the fatty by manipulating levels of different nutrients consumed during growth, and with pharmacological agents which alter the levels of insulin, fatty acid synthesis and fat deposition in the fatty rat. Since the metabolic profile of the fatty rat undergoes abnormal changes in response to a fast, the food motivation and sweet preferences of the fatty will be examined as a function of fasting levels, nutritional manipulations, and hormonal intervention. The results of these studies may suggest interventions which would prevent the complete development of hypercellular obesity and/or attenuate the "rebound" so often seen after weight reduction in both animal and man.